The Ontario Provincial Police will be texting 7,500 cellphone users who were in the vicinity of a murder victim last December, hoping someone can offer information to help solve the cold case.

But legal experts say the police may be on shaky legal ground if the text canvass produces any evidence, and that there are no clear rules about what happens to the data once the investigation wraps.

Homicide investigators were granted a court order that forced cellphone companies to turn over the phone numbers of their customers whose devices pinged a cell tower in an area where a murder victim was last seen alive. The OPP says it was not given the names or any other contact information for the cellphone users.

The OPP calls the move “an innovative new technique to identify potential witnesses” in the investigation into the murder of Frederick “John” Hatch, 65. His partially burned body was found Dec. 17, 2015 near Erin, Ont., northeast of Guelph. The Toronto man, who was known to hitchhike, was last seen alive the day before in a discount store in the area of West Hunt Club Road and Merivale Road in Nepean, outside of Ottawa.

About 7,500 cellphone numbers identified to have been in use in the vicinity of that area on Dec. 16, 2015 between 12:30 p.m. and 3:30 p.m. will receive two text messages from the OPP on Oct. 27. The messages, one in English and one in French, will ask the recipients to visit a website and voluntarily answer questions.

Anyone who receives the message can also call the OPP’s tip line at 1-844-677-5010 to speak directly with a homicide investigator.

“Building on the accepted practice of the door-to-door witness canvass, texting is an evolution of this investigative technique that is unique, maybe unprecedented,” said Det. Insp. Andy Raffay of the criminal investigation branch.

“(I)t’s the most efficient way to contact these people quickly to either eliminate them as witnesses or learn whether they have any useful information.”

The text message canvass will potentially reach witnesses who may not be aware of Hatch’s murder “but they may help us solve it by volunteering information and potentially remove a dangerous offender from society before they harm someone else,” said Det. Supt. Dave Truax, director of criminal investigation services.

Lawyer: ‘Fishing expeditions’ aren’t allowed

Michael Spratt, a partner at Abergel Goldstein and Partners law firm in Ottawa, says if the text canvass produces any fruitful information, police may find it’s not admissible in court.

“There is some concern here because police aren’t permitted to engage in groundless fishing expeditions… There has to be reasonable grounds to believe the information being sought will afford evidence of an offence.”

He said it’s clear from what investigators have said publicly in this case that they have “no idea” what this technique could produce.

“They may be on constitutionally shaky ground because this seems like a fishing expedition for digital information.”

Forcing a phone carrier to release information is much different than knocking on a door during a canvass, Spratt said.

“This is akin to knocking on everyone’s door and then looking in their mailboxes and opening their mail to see if there is anything of use.”

What happens to the data?

An Ontario Superior Court judge ruled in January that police conducting these searches – sometimes referred to as “tower dumps” – must only seek the minimal amount of information necessary to properly carry out the search.

The precedent-setting decision created important guidelines for police to follow in these sorts of digital searches, said Laura Berger, a staff lawyer with the Canadian Civil Liberties Association.

“The police have to narrowly define their request rather than seek an overbroad production order that would result in the disclosure of masses of information. These production orders have to be tailored to the information that police truly need to advance the investigation,” Berger told CTVNews.ca.

After the ruling, questions linger about what happens to the court-obtained cellphone data once police are finished with it.

“We have a situation where police can obtain this information, but it’s unclear how they retain it and whether they will be using it for secondary purposes,” Berger said.

“It may be very well justified to collect information for a certain purpose. With technology these days, that information can be stored and accessed down the line in ways that weren’t originally anticipated.”

The CCLA would like to see a prohibition on secondary uses of the data, Berger said, adding that informational afterlife is a “live issue.”

The use of cellphone information is “in many way analogous to door knocking,” Berger said, but police should use clear language to ensure that any possible witnesses understand that they have a right to refuse information or not disclose their identity to law enforcement officials.

“So I think what makes sending a text message similar (to door-knocking) but raises similar concerns is the question of whether people will feel coerced or not,” she said.

“We would expect and want the language to make clear that people are not legally required to provide information or to identify themselves if they do follow that link and take a look at the website.”